This invention relates to the art of polysulfide polymers, more particularly to thiol terminated liquid polysulfide polymers and hot melt applications, such as, hot melt applied sealants, extrusion of hoses and the like.
The use of liquid thiol terminated polysulfide polymer in caulks, sealants and the like for numerous applications is well known. Such materials have normally, until now, been chemically cured in situ.
When rapid cure was desired, a two part system was necessary requiring mixing with proper equipment just before use. One part chemical cure, on the other hand, was satisfactory in avoiding the need for in situ mixing but inherently was a slower cure requiring that provision be made for time to reach structural integrity, in some uses requiring provision of storage facilities, support racks and the like. In production applications, the extra space and/or equipment required by either cure mechanism added a cost factor whose elimination would be considered desirable by those skilled in the art.
Hot melt applied materials offer the potential to eliminate both the two part chemical cure requirement of in situ mixing and the lengthy holding requirement of one part chemical cure.
Although polysulfide rubbers are classified along with most other natural and synthetic rubbers as thermoplastic materials, they have always been considered by the art as sharing the property of most rubbers that, once vulcanized, heating to the point at which plastic flow is possible, would cause irreversible degradation of the polymeric chain and that, upon cooling, the resulting properties would be far poorer. Illustrative of the thermal degradation process is an article by Bertozzi in Rubber Chemistry and Technology, Vol. 41 (1968) p. 114 at pages 128 through 130.
The ability to formulate a cured polysulfide rubber in such fashion that the good mechanical properties characteristic of polysulfide rubbers in general is retained after extrusion under heat and pressure is thus unexpected.
Cure of thiol terminated liquid polysulfide polymers with zinc compounds including zinc oxide and tetraalkylthiuram polysulfides is disclosed by Canadian Pat. No. 907,793, Aug. 15, 1972. The further inclusion of sulfur in this cure system is disclosed in U.S. Pat. No. 3,637,574, Jan. 25, 1972.
Neither patent suggests that the cured compositions disclosed therein will have hot plastic flow properties different from other known cured polysulfide rubbers.